Manchester City's Vincent Kompany was injured in the opening game of the Premier League season against Newcastle United. Photograph: Martin Rickett/PA

Vincent Kompany could be ruled out until October, with his availability for the derby meeting with Manchester United at the Etihad Stadium on 22 September in serious doubt due to his recovery from a groin injury taking longer than first hoped.

If he is unable to play again until next month, his first league appearance would be Everton's visit on 5 October, meaning Kompany would have missed five games in the competition since suffering the problem in City's 4-0 win over Newcastle Unitedat the Etihad Stadium in their opening match.

If Manuel Pellegrini, the manager, cannot select his captain for United's visit, he would have to decide whether Kompany should be risked for the trip to Aston Villa on 28 September. Yet given the injuries that have plagued him during the last two seasons Pellegrini may decide to pencil him in for Bayern Munich's visit on 2 October in the Champions League. Before the current issue Kompany injured his calf on three separate occasions.

After lasting only 71 minutes against Newcastle, Kompany hoped for a swift return, tweeting: "Injury is a blow after all the hard work. I'll be back to that level in no time. Thanks for all the support!"

But with the club's medical department advising a minimum of six weeks, Kompany may miss all of City's September programme, though there is no concern over his long-term prognosis.

Martin Demíchelis, who was bought from Atlético Madrid partly as cover for Kompany and following Kolo Touré's departure to Liverpool, has himself been ruled out for six weeks due to a knee injury. City, though, will not sign a free agent to replace the central defender, who joined for £3.5m on Sunday.

With Matija Nastasic available following an ankle issue, and Micah Richards close to returning from a hamstring injury, Pellegrini has sufficient options in central defence.Following the current international break City are at Stoke City on Saturday-week, before they travel to Viktoria Plzen in the opening Champions League group game before United's visit.